Over half of North American zinc shipments are used for the production of galvanized steel. There is a significant scrap rate in mills producing galvanized sheet (this can be on the order of 15 to 20%), and the scrap rate in the plants of primary fabricators of galvanized sheet can be as high as 25% or more. Thus, over one million tons of fresh galvanized scrap are produced each year.
Galvanized scrap is normally purchased by steel mills at a substantial discount to non-galvanized material. This discount is necessary because the galvanized scrap must be fed to melting furnaces where the zinc vaporizes and is trapped in the flue dust, with the result that this flue dust cannot be easily sold or recirculated to the furnace. Further, there are now environmental constraints on disposal of zinc containing dusts as land-fill. Also, feeding excessive amounts of galvanized scrap to basic oxygen steel-making furnaces (BOF) can result in costly shut-downs for cleaning and refractory repair. Thus, there is great interest in development of an economical method of removing zinc from galvanized scrap. Although no process has been transferred as of now to successful commercial practice, at least six approaches have been described: